Studies on myocardial amino acid metabolism are proposed and based on two recent observations: a) Clinical investigations in patients with and without coronary artery disease have indicated that amino acids can be either utilized or released by the human myocardium, and b) studies using in vitro preparations have shown that amino acids participate in the metabolic response to myocardial hypoxia resulting in production of alanine (from glycolysis) and succinate (from breakdown of aspartate and/or glutamate). The proposed studies will examine the relationship between citric acid cycle intermediates and amino acid metabolism in quiescent papillary muscles. A isolated working heart preparation has been adopted which allows to correlate metabolic activity to the functional state of the heart in experiments lasting three hours. The working heart preparation will be used in studies on amino acid utilization, oxidation of amino acids and metabolism of amino-nitrogen . The results of these studies will contribute to a more detailed understanding of the factors regulating myocardial amino acid metabolism.